This invention relates to articles composed of resinous polymers of acrylonitrile (AN) and methacrylonitrile (MAN) and particularly to multiaxially oriented articles and more particularly to multiaxially oriented films of copolymers of acrylonitrile and methacrylonitrile.
Polyacrylonitrile (PAN) has excellent barrier properties, chemical resistance, rigidity, and heat resistance. PAN, however, is not a thermoplastic, and must be dissolved in a solvent in order to be processed. The use of a solvent negatively affects the polymer's barrier properties.
Polymethacrylonitrile (PMAN) also has desirable barrier properties, chemical resistance, and rigidity although they are not as good as those of PAN. In contrast to PAN, PMAN is a melt processable thermoplastic, but it is prone to de-polymerization at high temperatures.
In this invention, copolymers of AN and MAN have been formed to obtain the best properties of both PAN and PMAN. A copolymer of these nitriles results in an article having excellent barrier properties, chemical resistance, rigidity and heat resistance. while desirable thermoplastic properties such as melt stability for melt processing are also obtained.
Prior to this invention, copolymers of AN and MAN were formed using only small amounts of AN, because polymers made with more than 20% by weight of polymerized acrylonitrile could not be extruded. For example, it is taught in U.S. Pat. No. 3,565,876 that up to about 20% by weight of acrylonitrile can be copolymerized with methacrylonitrile to form extrudible copolymers which can be readily oriented and possess excellent physical properties. Increasing the acrylonitrile content above 20% by weight in acrylonitrile/methacrylonitrile copolymers resulted in a resin which was unstable and not processable by any of the usual commercial techniques known today, including extrusion. Although the copolymers of the U.S. Pat. No. 3,565,876 had desirable qualities, their low AN content failed to take full advantage of AN's superior barrier characteristics.
In this art, therefore, it is desirable to have a processable, stable acrylonitrile/methacrylonitrile copolymer system wherein the acrylonitrile content is greater than 20% of the final polymer composition.